Virus-Sized Laser Defies Diffraction Limit

EVANSTON, Ill., Nov. 6, 2012 — The bow tie is a popular shape for pasta and maybe soon it will be for laser cavities, too.

Single-laser devices the size of virus particles operate at room temperature and defy the diffraction limit, thanks to a lasing cavity composed of 3-D bow-tie-shaped metal nanoparticle dimers. The plasmonic nanolaser, designed at Northwestern University, could be integrated into silicon-based photonic devices, all-optical circuits and nanoscale biosensors.

Reducing the size of photonic and electronic elements is critical for ultradense information storage and ultrafast data processing. Miniaturizing a key workhorse instrument — the laser — is no exception.

“Coherent light sources at the nanometer scale are important not only for exploring phenomena in small dimensions but also for realizing optical devices with sizes that can beat the diffraction limit of light,” said Teri Odom, a materials science and engineering professor at the university’s McCormick School of Engineering and Applied Science. “The reason we can fabricate nanolasers with sizes smaller than that allowed by diffraction is because we made the lasing cavity out of metal nanoparticle dimers.”

These metal nanostructures support localized surface plasmons, which have no fundamental size limits when confining light.

Bow-tie geometry offers plasmon lasers two significant benefits compared to previous designs: First, because of an antenna effect, the bow-tie structure provides a well-defined electromagnetic hot spot in a nanosized volume; secondly, because of its discrete geometry, the individual structure has only minimal metal “losses.”

“Surprisingly, we also found that when arranged in an array, the 3-D bow-tie resonators could emit light at specific angles according to the lattice parameters,” Odom said.